Monolithically integrated 112 Gbps PAM4 optical transmitter and receiver in a 45†nm CMOS-silicon photonics process.

We demonstrate a transmitter and receiver in a silicon photonics platform for O-band optical communication that monolithically incorporates a modulator driver, traveling-wave Mach-Zehnder modulator, control circuitry, photodetector, and transimpedance amplifier (TIA) in the GlobalFoundries Fotonix (45SPCLO) platform. The transmitter and receiver show an open 112 Gbps PAM4 eye at a 4.3 pJ/bit energy efficiency, not including the laser. Extensive use of gain-peaking enables our modulator driver and TIA to achieve the high bandwidths needed in the 45 nm CMOS-silicon photonics process. Our results suggest an alternative to the frequent approach of bump-bonding BiCMOS drivers and TIAs to silicon photonics.

Tailoring Mixed-Halide, Wide-Gap Perovskites via Multistep Conversion Process.

Wide-band-gap mixed-halide CH3NH3PbI3-XBrX-based solar cells have been prepared by means of a sequential spin-coating process. The spin-rate for PbI2 as well as its repetitive deposition are important in determining the cross-sectional shape and surface morphology of perovskite, and, consequently, J-V performance. A perovskite solar cell converted from PbI2 with a dense bottom layer and porous top layer achieved higher device performance than those of analogue cells with a dense PbI2 top layer. This work demonstrates a facile way to control PbI2 film configuration and morphology simply by modification of spin-coating parameters without any additional chemical or thermal post-treatment.

Quantifying Geometric Strain at the PbS QD-TiO2 Anode Interface and Its Effect on Electronic Structures.

Quantum dots (QDs) show promise as the absorber in nanostructured thin film solar cells, but achieving high device efficiencies requires surface treatments to minimize interfacial recombination. In this work, lead sulfide (PbS) QDs are grown on a mesoporous TiO2 film with a crystalline TiO2 surface, versus one coated with an amorphous TiO2 layer by atomic layer deposition (ALD). These mesoporous TiO2 films sensitized with PbS QDs are characterized by X-ray and electron diffraction, as well as X-ray absorption spectroscopy (XAS) in order to link XAS features with structural distortions in the PbS QDs. The XAS features are further analyzed with quantum simulations to probe the geometric and electronic structure of the PbS QD-TiO2 interface. We show that the anatase TiO2 surface structure induces PbS bond angle distortions, which increases the energy gap of the PbS QDs at the interface.

Increased Quantum Dot Loading by pH Control Reduces Interfacial Recombination in Quantum-Dot-Sensitized Solar Cells.

The power conversion efficiency of quantum-dot-sensitized solar cells (QDSSCs) hinges on interfacial charge transfer. Increasing quantum dot (QD) loading on the TiO2 anode has been proposed as a means to block recombination of electrons in the TiO2 to the hole transport material; however, it is not known whether a corresponding increase in QD-mediated recombination processes might lead to an overall higher rate of recombination. In this work, a 3-fold increase in PbS QD loading was achieved by the addition of an aqueous base to negatively charge the TiO2 surface during Pb cation deposition. Increased QD loading improved QDSSC device efficiencies through both increased light absorption and an overall reduction in recombination. Unexpectedly, we also found increased QD size had the detrimental effect of increasing recombination. Kinetic modeling of the effect of QD size on interfacial charge transfer processes provided qualitative agreement with the observed variation in recombination lifetimes. These results demonstrate a robust method of improving QD loading, identify the specific mechanisms by which increased QD deposition impacts device performance, and provide a framework for future efforts optimizing the device architecture of QDSSCs.

Interface Engineering in Inorganic-Absorber Nanostructured Solar Cells.

Nanostructured solar cells have the potential to provide a low-cost alternative to more traditional thin film solar cell technologies. Of particular interest are nanostructured solar cells with inorganic semiconductor absorbers, due to their favorable absorption properties. Such devices include quantum-dot-sensitized solar cells (QDSSCs), extremely thin absorber solar cells (ETASCs), and colloidal quantum dot solar cells (CQDSCs). However, these device architectures suffer from high rates of internal recombination and other problems associated with their extensive internal surface areas. Interfacial surface treatments have proven to be a highly effective means to improve the electronic properties of these devices, leading to overall gains in efficiencies. In this Perspective, we focus on three types of interfacial modification: band alignment by molecular dipole layers, improved CQD film mobilities by ligand exchange, and reduced recombination by interfacial inorganic layers. Select examples in each of these categories are highlighted to provide a detailed look at the underlying mechanisms. We believe that surface modification studies in these devices-QDSSCs, ETASCs, and CQDSCs-are of interest not only to these fields, but also to the broader photovoltaics community.

Regulation of the transient receptor potential channel TRPA1 by its N-terminal ankyrin repeat domain.

The transient receptor potential channel A1 (TRPA1) is unique among ion channels of higher vertebrates in that it harbors a large ankyrin repeat domain. The TRPA1 channel is expressed in the inner ear and in nociceptive neurons. It is involved in hearing as well as in the perception of pungent and irritant chemicals. The ankyrin repeat domain has special mechanical properties, which allows it to function as a soft spring that can be extended over a large range while maintaining structural integrity. A calcium-binding site has been experimentally identified within the ankyrin repeats. We built a model of the N-terminal 17 ankyrin repeat structure, including the calcium-binding EF-hand. In our simulations we find the calcium-bound state to be rigid as compared to the calcium-free state. While the end-to-end distance can change by almost 50% in the apo form, these fluctuations are strongly reduced by calcium binding. This increase in stiffness that constraints the end-to-end distance in the holo form is predicted to affect the force acting on the gate of the TRPA1 channel, thereby changing its open probability. Simulations of the transmembrane domain of TRPA1 show that residue N855, which has been associated with familial episodic pain syndrome, forms a strong link between the S4-S5 connecting helix and S1, thereby creating a direct force link between the N-terminus and the gate. The N855S mutation weakens this interaction, thereby reducing the communication between the N-terminus and the transmembrane part of TRPA1.